1. Field of the Invention
The present invention relates to a process for the electrochemical reduction of organic compounds.
2. Description of the Background
The electrochemical reduction of organic compounds has hitherto been used on an industrial scale only in exceptional cases, eg. for the cathodic dimerization of acrylonitrile. Because current densities were inadequate in economic terms, which meant that space-time yields (STY) were too small, current yields were too low, hydrogen was being formed, selectivities with a view to a number of possible reduction steps were too low, the special catalytically active cathodes were not sufficiently available on a technical scale and/or the on-stream times of the catalytically active cathodes were too short, it has hitherto not been possible for electrochemical reduction on cathodes to be utilized industrially.
A computer-assisted simulation for electrochemical hydrogenation of glucose is described by V. Anantharaman et al. in J. Electrochem. Soc., 141, (1994) pp. 2742-2752, the results of this simulation being compared with experimental data by K. Park et al. which were published in J. Electrochem. Soc., 132, (1985) pp. 1850 et seq. and J. Appl. Electrochem., 16, (1986) pp. 941 et seq.. As can be gathered from this publication this reaction, which is carried out using a continuous reactor comprising a sintered-glass disk and powdered Raney nickel embedded therein as the electrically conductive substance as the cathode, likewise generates hydrogen.
It is also known, from publications on preparative organic electrochemistry (eg. Electrochimica Acta, 39, (1994) pp. 2109-2115) that anodes and cathodes used in preparative electrochemistry must have special electrochemical characteristics. Such electrodes are often fabricated by metallic or carbonaceous support electrodes being coated by means of suitably adapted coating methods such as plasma spraying, impregnation and stoving, hot pressing etc. (see, instead of many, EP-B 0 435 434).
A drawback of these established fabrication methods is that the electrodes, after inactivation of the catalytically active layer, often have to be removed from the electrolytic apparatus and subjected to external regeneration, so that short catalyst on-stream times preclude economic utilization of the electrochemical synthesis system. A further drawback consists in the laborious preparation of the catalytically active layer as such and the difficulties in achieving adequate bonding to the support electrode. The development effort for a classic electrode coating process can in many cases be justified in economic terms only with major industrial processes such as chlorine-alkali electrolysis or the cathodic dimerization of acrylonitrile. The use of commercially heterogeneous catalysts is often not a practical option, because thermal transformation in the case of thermal coating processes or masking of the active regions in the case of cold-bonding processes cannot be precluded.
A catalytically active electrode, which is constructed as a perfused filter layer comprising a suspension of finely disperse catalyst material on a porous base body, is used according to EP-B 0 479 052 in a process for separating metal ions from process waters and effluents.